In the manufacturing process of semiconductor devices (e.g., LSIs and SLSIs) or liquid crystal display panels, light is applied through a mask (photomask) to print patterns. When any particle is attached to the mask, it may absorb or deflect the radiation and cause deformation of features or makes the edge of the features rugged, resulting in poor dimensional accuracy, poor quality and poor appearance. To avoid this problem, a pellicle with good light transmittance is attached to the mask surface so as to prevent possible attachment of particle to the mask surface.
A pellicle usually has a metallic pellicle frame and a pellicle membrane attached with an adhesion to one end surface of the frame. The other end surface of the pellicle frame has an adhesion layer for fixing the pellicle to a photomask. The adhesive layer is protected by, for example, sheet-shaped material having releasability (separator).
A pellicle that has been checked for the absence of any particle on the pellicle membrane is shipped or transported while being hermetically packaged in a given container under strict conditions so as to avoid inclusion of particle.
The pellicle frame is usually made of aluminum alloy. Among other aluminum alloys, black anodized aluminum alloy has been employed in order to meet the requirements indispensable for pellicles: 1) black color for preventing stray light; 2) lightness and high strength; 3) high surface hardness; and so forth.
The black anodized layer formed on the aluminum alloy surface has many asperities on the surface and is porous, hard and brittle. Thus, in some cases, force and vibration generated during the manufacturing process of a pellicle, or frictional force between the shipping case and pellicle frame generated during the transportation of the pellicle cause dust generation due to scattering of dust and black pigment particles present on the asperities or in the pores of the black anodized layer or due to destruction of the brittle black anodized layer surface.
One proposed method of preventing such dust generation is to smooth the entire surface of a pellicle frame by dip coating with a non-adhesive transparent organic polymer or non-adhesive transparent fluorine organic polymer, which have good light resistance (see, e.g., Patent Literature 1).
Another proposed method is to form acrylic resin coating on the surface of an aluminum pellicle frame by cationic electrodeposition coating (see, e.g., Patent Literature 2).
Still another proposed method is to electrodeposit polymer coating such as acrylic resin or epoxy resin coating on the surface of an aluminum pellicle frame (see, e.g., Patent Literature 3).